Exhaust gases emitted by internal combustion engines generally contain particulate matter (PM) containing mainly carbon, and ash containing non-combustible components, and the like and these are known to be a cause of atmospheric pollution. In this regard, regulations have been tightened year by year for emissions of particulate matter in addition to components contained in exhaust gases, such as hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx). Because of this techniques have been proposed for trapping and removing such particulate matter from exhaust gases.
For example, a particulate filter for trapping this type of particulate matter can be provided in the exhaust pathway of an internal combustion engine. For example, because gasoline engines emit certain amounts of particulate matter, although less than diesel engines, together with exhaust gases, a gasoline particulate filter (GPF) is, in some cases, installed in the exhaust pathway. A filter in which a substrate is constituted from a multiplicity of cells made up of a porous material and the entry and exit of the multiplicity of cells are alternately blocked, which is a structure known as a wall flow structure, is known as this type of particulate filter (see Patent Literature 1 and 2). In a particulate filter having a wall flow structure, exhaust gas flowing in from the entry of a cell passes through a porous cell partition that divides the cells, and is discharged to a cell exit. Then, while the exhaust gas passes through the porous cell partition, particulate matter is trapped in pores inside the partition.